muduo之CountDownLatch.cc

        CountDownLatch用线程同步的。

CountDownLatch.h

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#ifndef MUDUO_BASE_COUNTDOWNLATCH_H
#define MUDUO_BASE_COUNTDOWNLATCH_H

#include "muduo/base/Condition.h"
#include "muduo/base/Mutex.h"

namespace muduo
{
//对	Condition(条件变量)的封装,通过倒计时计数器的方式，设置计数
class CountDownLatch : noncopyable
{
 public:

  explicit CountDownLatch(int count);				//count是线程的数量
  void wait();

  void countDown();

  int getCount() const;

 private:						//CountDownLatch由一把锁，条件变量，计数器构成
  mutable MutexLock mutex_;
  Condition condition_ GUARDED_BY(mutex_);
  int count_ GUARDED_BY(mutex_);//count是线程的数量
};

}  // namespace muduo
#endif  // MUDUO_BASE_COUNTDOWNLATCH_H

CountDownLatch.cc

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#include "muduo/base/CountDownLatch.h"

using namespace muduo;

CountDownLatch::CountDownLatch(int count)//倒计时计数器
  : mutex_(),
    condition_(mutex_),				//初始化，条件变量用成员锁初始化
    count_(count)
{
}

void CountDownLatch::wait()
{
  MutexLockGuard lock(mutex_);
  while (count_ > 0)			//只要计数值大于0，CountDownLatch类就不工作，知道等待计数值为0
  {
    condition_.wait();
  }
}

void CountDownLatch::countDown()			//倒数，倒计时
{
  MutexLockGuard lock(mutex_);
  --count_;
  if (count_ == 0)
  {
    condition_.notifyAll();
  }
}

int CountDownLatch::getCount() const			//获得次数
{
  MutexLockGuard lock(mutex_);
  return count_;
}

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